Direct Gluing Vinyl Sheet and Tile to OSB Subfloors

Installing a glue down vinyl floor (sheet or tile) directly over Oriented Strand Board (OSB) Subflooring has become a hot topic for me of lately. I have had people asking about installing sheet LVT, and VCT directly to the OSB Subfloor without the use of an underlayment.

Most flooring vinyl flooring manufacturers do not allow direct glue down directly to the subfloor. If you noticed, I said most. IVC says you can direct glue down to Oriented Strand Board (OSB), all others say no. So, I researched this. First of all, IVC says the “OSB must be an underlayment panel and must be underlayment grade as specified and warranted by the manufacture”, not subfloor grade which is used in new home construction. IVC also states; Completely sand the floor with a floor sander, so that the floor is smooth and flat. Note: The chips in OSB overlap. Without sanding properly, OSB has high and low spots throughout the floor that could telegraph through the vinyl. Surface must then be primed using IVC FLEX-PRIM Acrylic Latex Primer.

So what exactly is Oriented Strand Board (OSB)?

Evolving from waferboard in the late 1970s, OSB is unique in that long wood strands are oriented, not randomly placed. Since its debut in 1978, OSB has been rapidly accepted. In fact, in many areas of North America, OSB has virtually replaced other panels in new residential construction today

OSB is manufactured from sustainable, fast-growing trees such as aspen poplar, southern yellow pine, mixed hardwoods, and other suitable species. Logs are cut to length, debarked, and processed into precise strands ranging from 3 1/2″ to 6″ long and approximately 1″ wide. The strands are dried, sorted, and mixed with wax and a waterproof exterior-type binder and formed into large continuous mats. These mats are oriented in cross directional layers for increased strength, and then pressed at a high temperature and pressure to form panels. Throughout this highly automated and fully engineered process, panels are monitored, tested, and certified to meet stringent quality standards for strength and uniformity.

My issue with direct glue down of vinyl sheet and tile flooring is that most/all OSB manufacturers recommend the panels be spaced for expansion and contraction. When installing over these spaced joints, you will have subfloor joint telegraphing. The questions then arise, can I patch these joints? Can I skim coat the OSB and make this acceptable? The answer for both is no. Patching or skim coating over these spaced joints will only cause failure. Sooner or later, these joints will move and flex and bust up the patch or skim coat leaving you with a failure all around the edges of these panels.

The other issue is OSB is made up of various wood chips. These chips swell differently and will cause show through when direct gluing to these panels. This is like gluing flooring to a layer of bark mulch!

I researched what the APA (American Plywood Association) and various OSB manufacturers require for spacing and for installation of glue down flooring. On the market today, there are several manufacturers of “Enhanced OSB” which promotes that their product is highly moisture resistant and will not swell at the joints. In my research, I looked at their edge spacing as well as their direct glue down flooring recommendations.

Spacing

Why must the OSB panels be spaced? All wood-based products will absorb or shed moisture, depending on the ambient relative humidity, including OSB. If the air is drier than the wood fiber, the OSB will shed moisture. If the air is more humid than the wood fiber, the OSB will absorb moisture.. This natural exchange will occur until the moisture content of the OSB and the humidity of the Ambient air are in equilibrium. Relative humidity can range widely, and the moisture content of an OSB panel can range from 6% to 14%. According to the APA, the total dimensional change for a 4.8’ panel can be 1/8 inch in width and length. (If the OSB gets soaking wet, the dimensional changes can be even greater.) When panels expand and impact one another, buckling can occur, so proper spacing and moisture control are keys to preventing buckling.

Per the APA, recommended spacing at end and edge joints is 1/8”, except when otherwise indicated by the manufacturer.

Per the OSB Guide; lightly butt tongue and groove panel sides together and leave 1/8″ gap at panel ends. Panel ends of single layer combination subfloor/underlayment should be lightly butted.

Installation of Glue Down Vinyl Flooring

All OSB manufacturers said the same thing; “for “Single-Layer Floors – great for use directly under carpet, light-weight concrete or hardwood flooring.” http://osbguide.tecotested.com/

LP TopNotch – Panels may be used in combination with an underlayment approved by the manufacturer to provide a surface that is suitable for the installation of resilient tile, sheet vinyl, or other finish flooring materials.

Bottom line is, flooring manufactures and even the OSB manufacturers’ do not recommend gluing vinyl sheet and tile flooring directly to these subfloor panels. A plywood underlayment should be installed between the structural subfloor of the actual foundation and the flooring material. Underlayments are meant to absorb the roughness, or imperfections of subfloors, so that the flooring can be installed on top of a smooth, hard surface that will give the flooring material extra support.

To me, direct gluing to Oriented Strand Board (OSB) is nothing more than a cost cutting measure that will come back to bite you and end up costing you more down the road after it fails and there is no warranty.